1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile etc. that includes an intermediate transferring body and that uses an intermediate transfer method.
2. Description of the Related Art
An intermediate transfer method is one of the widely used conventional methods for color image formation. In the intermediate transfer method, toner images of different colors that are formed on a plurality of photosensitive drums are overlapped and transferred to an intermediate transferring body, and then the toner images are collectively transferred to a transfer sheet. Because the photosensitive drums are serially provided opposite the transfer sheet or the intermediate transferring body, the intermediate transfer method is also called a tandem method. In the intermediate transfer method, an electronic copying process is executed and includes formation of electrostatic latent image, printing etc. pertaining to yellow (Y), magenta (M), cyan (C), and black (B) colors in each photosensitive drum, and the resulting electrostatic latent images are transferred to a moving intermediate transferring body.
Japanese Patent Laid-Open Publication No. H8-152812 discloses a technology to prevent a slip between an intermediate transfer belt and a driving roller, in which the driving roller is made of a material of μ thickness such as rubber or a rubber coating, to overcome the aforementioned drawback. Japanese Patent Laid-Open Publication No. H10-268656 discloses a technology in which, an average friction coefficient pertaining to the contact surfaces of the driving roller and the intermediate transfer belt is maintained between 0.1 and 0.45, and a cleaning blade is disjunctively provided as a backup to the driving roller until a primary transfer of the last toner image is complete.
However, the aforementioned intermediate transfer method has the following drawbacks. Image formation by using the technology to overlap colors is extremely difficult. Especially occurrence of a slip between the intermediate transfer belt and the driving roller during a primary transfer results in a significant deviation in positions of each color, thereby resulting in a color drift.
In the technology disclosed in Japanese Patent Laid-Open Publication No. H8-152812, the driving roller made of a material of μ thickness such as rubber or a rubber coating is used to prevent the color drift, necessitating a technology to include the rubber coating on a metal shaft of the driving roller, thereby increasing the cost.
An image forming apparatus disclosed in Japanese Patent Laid-Open Publication No. H10-268656 uses a metal roller as the driving roller, and it is mentioned that “Occurrence of a slip between a driving shaft and the intermediate transfer belt is acceptable”. In other words, the technology emphasizes on avoiding the influence of shock during contact of the cleaning blade, but does not consider preventing occurrence of a slip between the driving shaft and the intermediate transfer belt.
Moreover, when including sensors for detecting patterns on the intermediate transfer belt, supporting the intermediate transfer belt with two spindles restricts the fixing positions of the sensors. In other words, a technology is needed which prevents occurrence of a slip between the intermediate transfer belt and the driving roller even if a cheap metal roller is used as the driving roller.